1. Field of the Invention
The invention relates to a strut suspension.
2. Description of the Related Art
Strut suspensions for vehicles are composed of a small number of components, and are lightweight. Therefore, the strut suspensions are widely used. In the strut suspensions, a strut includes a shock absorber. The upper end of the piston rod of the shock absorber is connected to a vehicle body via an upper support. The lower end of the outer tube of the shock absorber is fixed to a hub carrier. Also, a coil spring is provided around the shock absorber, and the upper end of the coil spring is connected to the vehicle body via an upper spring seat and a bearing. A virtual line that connects the upper portion of the shock absorber to the ball joint of a lower arm fitted to the hub carrier is referred to as “kingpin axis”. The strut and a vehicle wheel are steered around the kingpin axis.
PCT application international publication No. WO2002-040299 describes a strut suspension in which a lower bracket is provided between a bearing and a vehicle. The inner portion of the lower bracket in a vehicle-width direction protrudes downward with respect to the outer portion in the vehicle-width direction. As a result, the rotational axis of the bearing matches the kingpin axis. This suppresses generation of the steering moment around the kingpin axis (i.e., the moment that rotates the strut).
In another conventional structure, the absorber-axis of the shock absorber matches the rotational axis of the bearing. In this structure, the steering moment around the kingpin axis is in a permissible range defined to satisfy the performance requirement, only when the reaction-force line of the coil spring, which varies due to a manufacturing process, is in a narrow variation range. That is, the performance of the suspension is adversely influenced by the variations in the coil spring due to manufacturing variance (i.e., the suspension behavior is influenced by the variations in the coil spring). Therefore, a steering moment tends to be generated around the kingpin axis due to the variations in the reaction-force line of the coil spring. That is, the stability of the vehicle tends to deteriorate. Accordingly, it is desirable to reduce the influence that the variations in the coil spring due to manufacturing variance have on the suspension.
Meanwhile, in the case where the rotational axis of the bearing matches the kingpin axis as in the strut suspension described in the aforementioned publication, the friction around the kingpin axis is extremely low, and therefore the steering moment around the kingpin axis is substantially zero. However, the steering feeling may deteriorate.